1. Field of the Invention
This invention relates to sheet feed apparatus for intermittently advancing a sheet of material, such as a thermoplastic web, and more particularly to high speed sheet feed mechanism including a compound drive crank.
2. Description of the Prior Art
Thermoforming apparatus, such as that illustrated in U.S. Pat. No. 3,346,923 has been provided heretofore for forming three dimensional objects from a generally continuous web of thermoplastic material. Such apparatus includes a heating oven for heating the sheet of material and differential pressure molds for forming a three dimensional article in the web. Trim press apparatus, such as that disclosed in U.S. patent application Ser. No. 142,241, entitled High Speed Trim Press, filed in U.S. Patent Office on Apr. 21, 1980 and assigned to the assignee of the present application, may be provided for subsequently severing the three dimensional articles from the web or sheet.
Apparatus such as that disclosed in the aforementioned patent application Ser. No. 142,241, which is incorporated herein by reference, discloses sheet feed mechanism for advancing the sheet to a trim press. The sheet feed mechanism includes vertically reciprocal sheet engaging fingers which, on a downward stroke incrementally downwardly advance the sheet.
If a conventional flywheel driven crank is utilized to drive the sheet engaging fingers in a to-and-fro path, the speed of operation is restricted because of the substantial mass of the conventional flywheel driven crank arm. At certain high speeds, such conventional flywheel driven crank arms also impart vibration to the machine. Accordingly, it is an object of the present invention to provide a new and novel high speed feed mechanism for advancing a sheet, such as a thermoplastic sheet.
Another object of the present invention is to provide a crank operated sheet feed system which reduces the imbalance otherwise set up with a conventional crank drive.
A conventional crank arm requires a relatively large "window" in which to complete its movement. Accordingly, it is an object of the present invention to provide a compound crank which operates within a reduced "window".
Yet another object of the present invention is to provide a high speed sheet feed apparatus comprising a compound crank including a pair of pivotally coupled crank arms which rotate between co-extensive or folded positions and longitudinally extended positions.
It is another object of the present invention to provide high speed sheet feed apparatus of the type described including sheet engaging mechanism which moves in a to-and-fro path to advance a sheet and mechanism for driving the sheet engaging mechanism including a stationary shaft, a movable, concentric shaft rotatably mounted on the stationary shaft, a crank arm fixed to the movable shaft, a secondary crank arm rotatably mounted on the primary crank arm, mechanism coupling the primary and secondary crank arms for concurrent rotary movement in opposite directions, and mechanism for pivotally coupling the secondary crank arm to the sheet engaging mechanism.
Still another object of the present invention is to provide high speed sheet feed apparatus comprising a compound crank drive including a rotatable primary crank arm and a secondary crank arm rotatably mounted on the primary crank arm for orbital movement therewith and for rotating motion relative thereto at a velocity equal to twice the rotational velocity of the primary crank arm.
Another object of the present invention is to provide high speed compound crank sheet feed apparatus which will decrease the cost of tooling.
Variations in the dimensions of the plastic sheet, and in particular foam sheets, due to temperature differentials and the like, sometimes results in nonuniform spacing between the articles formed in the sheet. Accordingly, it is an object of the present invention to provide compound crank sheet feed apparatus including mechanism for incrementally adjusting the crank mechanism to accurately align the articles to be trimmed with a work station, such as the trim station of a trim press.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.